Ki Longfellow, born Baby Kelly, was an American novelist, playwright, theatrical producer, theatre director, and entrepreneur with dual citizenship in Britain. She is best known in the United States for her novel The Secret Magdalene (2005), the first of her works exploring the divine feminine. In England, she is likely best known as the widow of Vivian Stanshall, musician and lead singer of the Bonzo Dog Doo-Dah Band.

The first of her novels to be published, China Blues (1989), and Chasing Women (1993) are mysteries and thrillers. In April 2013, the first of her Sam Russo Mysteries was published, part of a noir series set in and around New York City in the late 1940s. The fourth in the Sam Russo Mysteries was published in 2015. Walks Away Woman, about a neglected Arizona housewife walking out into the Sonoran Desert to die, was published in December 2013.

On January 26, 2018, Longfellow's memoir of her husband, The Illustrated Vivian Stanshall, a Fairytale of Grimm Art, illustrated by Ben Wickey, was published.

Ki Longfellow, born on Staten Island, New York, to a French-Irish mother and an Iroquois father, grew up in Hawaii and Marin County, California, but ended up living in France and England for many years. In England, she created and sailed the Thekla, a 180-foot Baltic Trader, to the port of Bristol where it became the Old Profanity Showboat. It remains there today as a Bristol landmark.

On it, she and Vivian wrote and staged a unique musical for the sheer joy of it. "Stinkfoot, a Comic Opera", garnered a host of delighted, if slightly puzzled, national reviews.